Core antigen protein of hepatitis C virus, and diagnostic method and kit using the same

Abstract

 The invention relates to DNA molecules, polypeptides expressed by them and their use in diagnosis and their methods of production. More particularly, it relates to a diagnostic DNA molecule, a diagnostic protein, diagnostic antibodies and protective antigen and antibodies for hepatitis C virus (HCV). The DNA molecule disclosed herein is characterized by the DNA molecule derived from the genome of an HCV, and coding for a polypeptide having the antigenicity of an HCV core antigen protein. The polypeptide may be used in the detection of HCV.

Description

TECHNICAL FIELD OF INVENTION

[0001] The invention relates to a DNA molecule, a polypeptide expressed by the molecule and their use in diagnosis and their methods of production. More particularly, it relates to a diagnostic DNA molecule, a diagnostic protein, diagnostic antibodies and a protective polypeptide for hepatitis C virus.

BACKGROUND OF THE INVENTION

[0002] Most cases of hepatitis arising from blood transfusion are viral-inducted, and distinguishable from other forms of viral-associated liver diseases caused by known hepatitis viruses such as hepatitis A virus (HAV) and hepatitis B virus (HBV). The etiological agent(s) of said Non-A, Non-B hepatitis (NANBH) has long been sought by many research groups and is presently believed to be the hepatitis C virus (HCV). Post-transfusion hepatitis (PTH) occurs in approximately 10% of transfusion patients, and NANBH accounts for up to 90% of these cases. The major problem in this disease is the frequent progression to chronic liver damage (25-55%). Therefore, the demand for sensitive, specific methods for detecting HCV in contaminated blood or blood products is significant.

[0003] The hepatitis C virus (HCV) was first identified by molecular cloning and characterization of its RNA genome by Choo, et al. (Science 244: 359-362, 1989). A specific assay by using said HCV antigen, designated C100-3, synthesized by the recombinant DNA method in yeast, was also developed for detection of the antibody of HCV (Science 244: 362-364). A detailed description regarding the genome of HCV, the cDNA sequences derived therefrom and polypeptides derived from said HCV genome or from HCV cDNA as well as methodologies, was given in EP 0 318 216 A1 in the name of Chiron Corporation. In particular, the European patent provides a synthesized polypeptide, C100-3 containing 363 viral amino acids which can be used for the detection of HCV antibodies. Now, kits for detecting HCV antibodies on the basis of C100-3 have been commercialized by Abbott Laboratories.

[0004] As suggested in the above European patent, HCV may be a flavivirus or flavi-like virus. Generally, with respect to morphology, flavivirus contains a central nucleocapsid surrounded by a lipid bilayer. It is believed that hepatitis C virus protein is composed of structural proteins including a nucleocapsid (core) protein (C) and two glycosylated envelope proteins (E1, E2) and nonstructural proteins (NS1-5). However, the corresponding virus has not yet been isolated nor characterized. It is only confirmed that said C100-3 disclosed by Choo et al. is a protein encoded by part of the nonstructural regions 3-4 of the HCV genome.

[0005] Besides, an enzyme-linked immunosorbent assay (ELISA) was developed for serological diagnosis of hepatitis C virus (HCV) infection, by using said HCV core protein (p22) synthesized by a recombinant baculovirus by Chiba, et al. (Proc. Natl. Acad. Sci. USA 88:4641-4645, 1991). It was found that C100-3 antibody was not detected in all post-transfusion NANBH cases, probably because of the delayed response to C100-3 antigen. Such delayed response was considered to be due to the fact that the C100-3 is an HCV nonstructural protein. However, Chiba, et al. used an unglycosylated 22-kDa nucleocapsid (core) protein, and established an antibody detection system to develop a specific sensitive method for diagnosing HCV infection.

[0006] The invention discloses a DNA molecule coding for an HCV core antigen protein and provides an alternative of HCV antibody assay.

SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to provide a DNA molecule coding for a polypeptide displaying the antigenicity of a hepatitis C virus (HCV) core antigen protein. More specifically, the invention provides a DNA molecule derived from the genome of HCV. The DNA molecule was cloned from the plasma of a patient with hepatitis C via a Polymerase Chain Reaction (PCR) technique.

[0008] Portions of the DNA molecule are useful as probes to diagnose the presence of virus in samples. As well, the DNA molecule of the invention is capable of producing, in an appropriate host, viral polypeptides displaying the antigenicity of an HCV core antigen protein.

[0009] It is another object of the present invention to provide a polypeptide displaying the antigenicity of an HCV core antigen protein. Said polypeptide was produced by an appropriate host transformed with the DNA molecule of the invention.

[0010] Also, it is an object of the present invention to provide a process for producing a polypeptide displaying the antigenicity of an HCV core antigen protein. The process comprises incubating host cells transformed with an expression vector containing a DNA molecule of the invention.

[0011] Still, it is another object of the present invention to provide a method for detecting HCV antibodies in samples by using said HCV core antigen protein as a probe. The method may be carried out by immunoassay or Western blotting which is characterized by using said HCV core antigen as a probe, capable of binding to antibodies directed against HCV in samples, to form an antigen-antibody complex.

[0012] The invention also includes a method for detecting HCV antibodies in samples by using said HCV core antigen protein combined with an HCV nonstructural protein as probes.

[0013] It is yet object of the present invention to provide a kit for analyzing samples for the presence of HCV antibodies in samples, comprising said HCV core antigen protein. Specifically, a kit for immunoassay for detecting HCV antibodies comprises said HCV core antigen protein and a suitable solid phase.

[0014] It is another further object of the present invention to provide monoclonal and polyclonal antibodies directed against said HCV core antigen protein. Also included in the invention is the process for producing said antibodies by immunizing an animal with said HCV core antigen protein. A method for analyzing HCV in samples can be established by using the obtaining antibodies.

[0015] It is yet further object of the present invention to provide vaccines for prevention of HCV infection comprising an immunogenic polypeptide of the invention, or an inactivated preparation or an attenuated preparation thereof.

[0016] These and other objects, advantages and features of the present invention will be more fully understood and appreciated by reference to the written specification.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Fig. 1A shows the DNA sequence derived from the genome of HCV nucleocapsid region (SEQ ID No: 3) and part of the envelope region in accordance with the invention. The amino acid sequence of the polypeptide encoded therein is shown in Fig. 1B (SEQ ID No: 4).

[0018] Fig. 2 shows the structure of the expression vector pEN-2 constructed by inserting the cDNA coding for an HCV core antigen into a plasmid. The figure also shows the restriction map illustrating the significant features of the vector pEN-2.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention provides a DNA molecule coding for a polypeptide displaying the antigenicity of an HCV core antigen protein. The DNA molecule is isolated from nucleic acid sequences present in the plasma of an HCV infected patient which includes the steps of isolating the viral particles from the patient's plasma, extracting and purifying the viral nucleic acid sequences, and then cloning the desired DNA molecule via a Polymerase Chain Reaction (PCR) technique. The primers used for cloning are

(i)

(ii)

[0020] The cloned DNA molecule is subject to a hybridization with original HCV particles for identification. The molecule thus obtained is designated EN-80-2. The DNA sequence of the molecule EN-80-2 is given in Fig. 1A (SEQ ID No: 3). The DNA molecule is derived from the genome of HCV nucleocapsid and envelope regions and has 669bp.

[0021] Portions of the DNA molecule are useful as probes to diagnose the presence of HCV nucleic acids in samples.

[0022] The DNA molecule of the present invention is inserted into an appropriate vector to form an expression vector. The vector can be a plasmid, bacteriophage or other DNA sequence which is able to replicate in a host cell. The preferable vector is a plasmid with the promoter lac. Referring to Fig. 2, we have shown an expression plasmid, pEN-2, constructed by a vehicle plasmid and the DNA molecule of the present invention.

[0023] An appropriate host is transformed with an expression vector containing the DNA molecule of the invention and the polypeptide displaying the antigenicity of an HCV core antigen protein can be produced in the transformed host. A process for producing the polypeptide displaying the antigenicity of an HCV core antigen has been established.

[0024] The invention also provides a polypeptide displaying the antigenicity of an HCV core antigen protein. The amino acid sequence of the polypeptide is given in Fig. 1B (SEQ ID No: 4). The polypeptide has a molecular weight of about 25,000 as measured by electrophoresis through a sodium dodecyl sulfate-polyacrylamide gel and is deduced to have about 220 amino acids. The ability of the obtained polypeptide to bind to HCV antibodies is confirmed by Western Blotting. Obviously, the polypeptide is reactive with the sera of the patients with hepatitis C but not reactive with the sera of persons without hepatitis C. This fact suggests that the polypeptide capable of detecting the presence of HCV antibodies in samples holds a potential in diagnosis of hepatitis C. Besides, the polypeptides displaying the antigenicity of an HCV core antigen, or an inactivated preparation or an attenuated preparation thereof in an immunogenically effective amount can be formulated as vaccines for prevention of HCV infection.

[0025] The method for detecting HCV antibodies in samples is included in the invention. The method is characterized by the HCV core antigen's capability of binding to HCV antibodies as a probe. The method can be carried out by immunoassay or Western Blotting. A preferred method is solid-phase immunoassay. The solid phase such as microtiter plates, beads and semipermeable membranes can be used to carry out the immunoassay. The substances as labels include enzymes, isotopes, fluorescent materials and any other materials which can be directly detected. The immunoassay is conveniently achieved by a Sandwich method. Particularly, an enzyme-linked immunosorbent assay (ELISA) was established. The ELISA comprises: 1) coating the polypeptide of the present invention onto a solid phase, 2) incubating a sample suspected of containing HCV antibodies with the polypeptide coated onto said solid phase under conditions which allow the formation of an antigen-antibody complex, 3) adding an anti-antibody (such as anti-IgG) conjugated with a label to be captured by the resulting antigen-antibody complex bound to the solid phase, and 4) measuring the captured label and determining whether the sample has HCV antibodies.

[0026] An alternative assay can be carried out by using the polypeptide of the invention combined with an HCV nonstructural protein as a probe. The assay is thought to be more specific and sensitive.

[0027] The invention still provides a kit for analyzing samples for the presence of HCV antibodies. The kit comprises a polypeptide of the invention and an appropriate solid phase wherein preferably, said polypeptide is coated to said phase.

[0028] The present invention provides monoclonal and polyclonal antibodies directed against said HCV core antigen protein. The antibodies are produced by using the polypeptide of the invention as an immunogen through standard procedures for preparing a hybridoma and/or conventional methods. The obtained antibodies are potential to develop a method for detecting HCV.

[0029] The following example is offered to aid in understanding of the present invention and are not to be construed as limiting the scope thereof.

EXAMPLES

I. Cloning of an HCV cDNA

[0030] The plasma of the patients infected with Hepatitis C virus are collected and ultracentrifuged at 4°C and then the viral particles are obtained. Subsequently, the viral nucleic acid (RNA) is extracted and purified by using guanidine isothiocyanate and acidic phenol from the viral particles.

[0031] The following oligonucleotide sequences :

(i)

(ii)

were used as primers in the subsequent cloning steps. A single-stranded antisense DNA molecule was produced using primer (ii) and reverse transcriptase and then the RNA template was replaced with the corresponding DNA molecule (using primer (i)) to produce a double stranded DNA molecule. The double stranded DNA molecule was amplified by the PCR method using Taq polymerase.

[0032] The cloned DNA molecule is subject to a hybridization with original HCV particle for identification. The obtained molecule is designated EN-80-2. The DNA sequence of the molecule EN-80-2 is given in Fig. 1A (SEQ ID No: 3). The DNA molecule is derived from the genome of HCV nucleocapsid and envelope regions and has 669bp.

II. Construction of a Plasmid Containing an HCV cDNA

[0033] The molecule EN-80-2 is treated with restriction endonucleases Bam HI and EcoRI to obtain a transposon containing said HCV cDNA. The obtained transposon is inserted into a vehicle plasmid which is first cleaved with restriction endonucleases Bam HI and EcoRI to obtain an expression plasmid, designated pEN-2. The expression of the HCV cDNA is under the control of a promoter lac. The structure of the expression plasmid pEN-2 and restriction map are given in Fig. 2.

III. Transformation of E. coli

[0034] The expression plasmid pEN-2 is incubated with E. coli BL21 (DE3) at 37°C overnight. The E. coli colonies producing HCV core antigen protein are selected by screening their expression products by Western Blotting. The selected clone, designated Clone EN-80-2, is exemplified by a culture deposited in American Type Culture Collection, MD, USA, on 14 July 1993 (Access Number ATCC 55451).

IV. Production of HCV Core Antigen

[0035] The transformed E. coli colonies are incubated in a conditioned culture medium. The colonies are centrifuged and lysed by freezing-defrosting cycles and enzyme-digestion. The protein product is released by the lysed cells and purified by chromatography. The purity of the obtained polypeptide is more than 90%.

[0036] The polypeptide has a molecular weight of about 25,000 as measured by electrophoresis through a sodium dodecyl sulfate-polyacrylamide gel.

V. Immunological Reactivity of HCV Core Antigen with HCV Antibodies by Western Blotting

[0037] The purified polypeptide is subject to an SDS electrophoresis by standard procedures. The SDS-PAGE gel is washed with deionized water at 4°C for 15 minutes and washed with Blotting Buffer (0.15M sodium phosphate buffer, pH 6.7) at 4°C for 20 minutes. The peptide map on the gel is then electroblotted onto a nitrocellulose paper under the Blotting Buffer at 1.3A for 1-1.5 hours. The paper is washed with Wash Buffer (PBS-Tween 20, pH 7.4) and blocked with Blocking Buffer (0.1M NaCl, 5mM EDTA, 50mM Tris, pH 7.2-7.4, 0.2% fetal bovine serum albumin, 0.05% Nonidet p-40, 1M urea) overnight.

[0038] The paper is reacted with the sera of the persons infected with/without hepatitis C which are first diluted with 40% NBBS/Tris-HCl (pH 7.4), 10X, at 40°C for 2 hours. After the reaction, the paper is washed with Wash Buffer three times. The paper is reacted with the anti-hIgG:HRPO conjugate (which is prepared as described hereafter) at 40°C for 2 hours. After the reaction, the paper is washed with Wash Buffer three times and then reacted with 10 ml Substrate Solution (0.01% 4-chloro-1-naphthol, 18% methanol, 0.04M Tris, pH 7.2-7.4, 0.1M NaCl and 0.01% H₂O₂) for 20 minutes. As shown in the Western blot, the polypeptide of the present invention is reactive with the sera of HCV patients but not reactive with the sera of healthy persons.

VI. ELISA for HCV Antibodies

[0039] 

(1) Treatment of Microtiter Plate
The microtiter plate is coated with the purified polypeptide of the invention at appropriate concentrations and blocked with a buffer containing bovine serum albumin. The treated microtiter plate is stored at 2-8°C.

(2) Preparation of Anti-hIgG:HRPO Conjugate
The purified anti-human Immunoglobulin G (anti-hIgG) is conjugated with horse radish peroxidase (HRPO) using NaIO₄ to obtain the anti-IgG:HRPO conjugate. The conjugate is purified by chromatography.

(3) Components of Reagents

(a) Wash Solution: Phosphate Buffer containing 0.9% NaCl and Thimerosal.

(b) Anti-hIgG:HRPO Conjugate Solution: the anti-hIgG:HRPO conjugate prepared as described above dissolved in Tris Buffer containing a proteineous stabilizer and antiseptics.

(c) Sample Diluent: Tris Buffer containing a proteineous stabilizer and antiseptics.

(d) OPD Substrate Solution: o-phenylene diamine (OPD) dissolved in citrate-phosphate buffer containing H₂O₂. (If the solution becomes orange, it means that the solution has been contaminated and cannot be used any more.)

(e) Stopping Solution: 2N H₂SO₄ solution.

(f) Positive/Negative Controls: the serum samples of persons infected with/without hepatitis C diluted with phosphate buffer containing a proteineous stabilizer and antiseptics at an appropriate concentration.

(4) Procedure:

(a) One hundred and fifty microliter (µl) of test samples diluted with Sample Diluent (1:10) and Positive/Negative Controls are added into the wells of the treated microtiter plate. Some wells have to be retained as substrate blanks.

(b) The plate is gently mixed by shaking and incubated at 37-40°C for 1 hour.

(c) The plate is washed with 0.3 ml of Wash Solution per well by a washer three times.

(d) One hundred µl of anti-hIgG:HRPO Conjugate Solution is added to each well.

(e) The plate is gently mixed by shaking and incubated at 37-40°C for 30 minutes.

(f) The plate is washed five times.

(g) One hundred µl of OPD Substrate Solution is added into each well and the plate is incubated at 15-30°C in the dark for 30 minutes.

(h) One hundred µl of Stopping Solution is added into each well and gently mixed to stop the reaction.

(i) The OD value per well is measured by a spectrophotometer at 492 nm.

(5) Determination:
The OD_492nm value per well subtracts the mean of the readings of the blanks (backgrounds). The difference (PCx-NCx) between the mean of the readings of the positive controls (PCx) and that of the negative controls (NCx) is equal to or more than 0.5.

[0040] The Cut-off value (CO) is calculated by the following formula:

[0041] When the readings of test samples are less than the CO value, the samples are considered negative (i.e. HCV antibodies cannot be detected in the samples).

[0042] When the readings of test samples are equal to or more than the CO value, the samples are expected to be positive; however, it is necessary to repeat the assay for the samples in duplicate. If the reading of either of the duplicate samples is less than the CO value, the samples are negative. If the duplicate samples are both more than or equal to the Cut-off value, the samples will be positive.

[0043] When the readings of test samples are more than NCx but less than the CO value by 20%, the samples should be regarded as questionable samples and the assay has to be repeated for those samples.

[0044] Twenty-seven samples were tested by the ELISA according to the invention. At the same time, the samples were also tested by the HCV antibody assay by using structural and nonstructural proteins as probes (i.e. Abbott's kit (II)). The comparison between the test results of Abbott's kit and those of the assay of the invention is given in Table I. It is noted that the results of Sample G 229 was negative by the Abbott's kit (II) but positive by the assay of the present invention. It is suggested that samples infected with HCV cannot be all detected by the Abbott's assay.

VII. Detection of HCV Antibodies by HCV Core Antigen Protein Combined with HCV Nonstructural Protein

[0045] The method is analogous to the ELISA as described above while HCV core antigen protein of the invention combined with an HCV nonstructural protein (9:1) is replaced for the HCV core antigen protein to be coated onto the plate.

[0046] Twenty-four samples were tested by the above-mentioned method. At the same time, the samples were also tested by Abbott's kit (II). The results are given in Table II. It is suggested that the results of the Abbott's assay is the same of the above-mentioned method.

VIII. Preparation of Antibodies against HCV

[0047] The antibodies against HCV core antigen protein can be produced by immunizing an animal with the core antigen protein according to the invention.

[0048] According to the standard procedure for producing monoclonal antibodies, a BAL-B/C mouse is immunized with the purified core antigen protein as described in Example II mixed with an adjuvant; and then the spleen cells are fused with mouse myceloma cells (FO cell line) using polyethylene glycol to form hybridoma cells. The desired clone producing monoclonal antibodies can be obtained by screening the titer of the antibodies produced by the hybridoma clones so prepared.

[0049] A diagnostic kit for detecting the presence of HCV in a sample, or a kit for determining if the HCV cells are successfully cultured can be developed by using the obtained antibodies associated with EIA and sandwich methods.

Claims

1. A DNA molecule coding for a polypeptide displaying the antigenicity of an HCV core antigen protein which is derived from the genome of nucleocapsid and part of envelope regions of an HCV, and degenerate sequences thereof.

2. A DNA molecule coding for a polypeptide displaying the antigenicity of an HCV core antigen protein comprising the DNA sequence as given in Fig. 1A (SEQ.ID NO:3), and degenerate sequences thereof.

3. A DNA molecule as claimed in claim 1 or claim 2 coding for an antigenically significant subfragment or variant of a polypeptide as defined in claim 1 or claim 2.

4. A DNA molecule according to any one of claims 1-3 which is cloned from the plasma of a patient infected with HCV.

5. Probes for Hepatitis C virus (HCV) nucleic acid which are derived from the DNA molecule according to any one of claims 1 to 4.

6. A DNA molecule according to any one of claims 1-3 capable of expressing a polypeptide displaying the antigenicity of an HCV core antigen protein in an appropriate host.

7. A process for cloning a DNA molecule according to any one of claims 1-3 which comprises isolating RNAs from hepatitis C patients' sera, and cloning said DNA molecule via a Polymerase Chain Reaction (PCR) technique.

8. A process according to claim 7 wherein the following sequences are used as primers:

(i)

(ii)

9. A polypeptide displaying the antigenicity of an HCV core antigen protein, which is encoded by the genome of nucleocapsid and part of envelope regions of hepatitis C virus, and derivatives thereof.

10. A polypeptide displaying the antigenicity of an HCV core antigen having the amino acid sequence as given in Fig. 1B (SEQ.ID NO:4), and derivatives thereof.

11. A polypeptide which comprises an antigenically significant subfragment or variant of a polypeptide as claimed in claim 9 or 10.

12. A polypeptide according to claim 9 or 10 having a molecular weight of about 25,000.

13. A polypeptide according to any one of claims 9-11 produced by an appropriate host transformed with the DNA molecule as defined in any one of claims 1-3.

14. A process for producing a polypeptide displaying the antigenicity of an HCV core antigen protein by the expression of a DNA molecule as defined in any one of claims 1-3.

15. A plasmid for expression of a polypeptide displaying the antigenicity of an HCV core antigen protein, designated pEN-2.

16. E. Coli transformed to produce a polypeptide displaying the antigenicity of an HCV core antigen protein, designated Clone EN-80-2 and deposited under Accession Number ATCC 55451.

17. A method for detecting HCV antibodies in samples, characterized by using a polypeptide as defined in any one of claims 9-11 as a probe, capable of binding to antibodies directed against an HCV antigen in samples to form an antigen-antibody complex.

18. A method according to claim 17, characterized by using a polypeptide as defined in any one of claims 9-11 combined with an HCV nonstructural protein as probes.

19. A kit for analyzing samples for the presence of HCV antibodies in samples, comprising a polypeptide as defined in any one of claims 9-11.

20. Antibodies or antigen binding fragments thereof directed against an HCV core antigen protein which are elicited by using a polypeptide as defined in any one of claims 9-11 as an immunogen.

21. A process for producing antibodies directed against HCV core antigen comprising immunizing an animal with a polypeptide as defined in any one of claims 9-11.

22. A method for analyzing HCV in samples characterized by using antibodies as defined in claim 20 as a probe.

23. Vaccines for prevention of HCV infection comprising an immunogenic polypeptide as defined in any one of claims 9-11, or an inactivated preparation or an attenuated preparation thereof.

Drawing